1. Field of The Invention
This invention relates to a negative electrode for secondary cells which utilizes carbon as an active material therefor and also to a non-aqueous electrolyte secondary cell comprising at least one electrode made of a carbon active material of the type mentioned above.
2. Description of The Prior Art
When using fine particles of crystalline carbon as an active material for negative electrode, the density of electric capacity becomes high, but a charge efficiency lowers or the crystal structure of the carbon material is destroyed presumably owing to the decomposition of a liquid electrolyte. To avoid this, there has been made an attempt described, for example, in Japanese Laid-open Patent Application No. 4-368778. In this application, the fine particles of crystalline carbon are individually covered with amorphous carbon produced by thermal decomposition of a gas such as of a hydrocarbon. As a consequence, the lowering of a charge efficiency and destruction of the carbon material can be prevented, while keeping the density of electric capacity at a high level.
However, full coverage of the fine particles of carbon with amorphous carbon produced by the thermal decomposition of a hydrocarbon or a gas of a hydrocarbon compound is very difficult. Eventually, it is inevitable to lower the charge efficiency or to destroy the carbon material as will be probably caused by the decomposition of a liquid electrolyte. In this way, it has been difficult to obtain a negative electrode for secondary cells which exhibits a high density of electric capacity.
Japanese Laid-open Patent No. 6-132027 proposes a method wherein fine particles of carbon used as an active material are mixed with a thermosetting resin and the mixture is sintered or fired to permit the thermosetting resin to be carbonized, thereby covering individual fine particles with the resultant amorphous carbon. In this method, the amorphous carbon formed by the carbonization of a thermosetting resin is so porous that it is difficult to fully cover the surfaces of the fine particles of carbon with the amorphous carbon.